1. Field of the Invention
This invention is related to a method for fabricating a working electrode of a dye-sensitized solar cell; particularly, a method for fabricating a working electrode of a dye-sensitized solar cell by electrophoresis.
2. Description of the Related Art
Under the dual problems of energy shortage and environmental protection, solar energy is considered to be a potential and environment-friendly energy. Because of the high cost of crystalline silicon solar cells, the development of dye-sensitized solar cells with low-cost electricity-generating elements is getting more and more notice.
Please refer to FIG. 1, the main inner structures of a dye-sensitized solar cell 100 comprises a working electrode (anode) 110, a counter electrode (cathode) 120 and an electrolyte 130. The anode 110 comprises a conductive substrate 111 and a photo-sensitive layer 112 for receiving solar energy; on the other hand, the cathode 120 comprises a conductive substrate 121 and a catalyst layer 122 with suitable thickness. Depending on the material of the substrate 113, 123 thereof, for instance, if the substrate 113, 123 is made of materials with non-conductive or relatively bad conductive, a conductive layer 114, 124 of a conductive material may be provided on the substrate 113, 123, respectively. The photo-sensitive layer 112 contains a semiconductor material adsorbed with a photo-excited dye. The main component of the electrolyte 130 is an organic solvent containing iodine and iodine ion.
Due to the simple structure of dye-sensitized solar cells, a flexible dye-sensitized solar cell can be obtained for broad application if a plastic plate or a Ti foil is used as the substrate 113, 123. Beside, the substrate 113, 123 can also be a glass.
Briefly, a working principle of dye-sensitized solar cells is: (1) the semiconductor material in the photo-sensitive layer is excited by a photon and then makes the dye thereon into an oxidation state for releasing electrons/holes; (2) the electron moves into the conductive material of the conductive substrate and transfer out through an external circuit; (3) the dye in oxidation state is reduced to ground state by the redox pair of the electrolyte; and (4) the electron transferring through the external circuit reduces the redox pair at cathode.
In order to broaden the development of the dye-sensitized solar cell industry, it is a key technique to eliminate the fabrication process of dye-sensitized solar cells. Adsorbing the dye onto the surface of the semiconductor material is the time-consuming step in the fabrication process of dye-sensitized solar cells. The most widely used method is to immerse a photoelectrode (i.e. a conductive substrate coated with a semiconductor material such as titanium dioxide) into a dye solution. The aforementioned method takes at least 10 hours to make the dye adsorb onto the surface of the semiconductor material on the photoelectrode completely and even takes 3˜5 hours to complete the adsorbing process while rising the working temperature to 50° C. Therefore, the time cost is not easy to control under this situation, and the development of dye-sensitized solar cell industry is adversely obstructed.